Peanut Butter

It takes about 850 peanuts to produce an 18-once jar of peanut butter, so a little of the stuff packs a powerful protein punch. Two tablespoons, about the size of a ping pong ball, is an appropriate serving size.

Baked Potatoes

When not covered in cheese and sour cream, potatoes aren't hard on the waistline and are high in potassium and vitamins C and B6. A perfectly portioned baked potato should be about the size of a computer mouse.

Cheese

A few cheese cubes and some fruit is the perfect mini-meal between lunch and dinner. To make sure you're noshing on the right amount, roll some dice. A serving of cheese is one ounce, or the size of six dice.

Oil

Cooking with heart-healthy oils is a great way to add flavor and nutrients to any dish, but it is easy to sometimes go overboard. Stick to about a teaspoon, or the size of one thumb tip, of oil per portion — a little can go a long way.